What does the difference in cylinder bore measurements taken parallel and perpendicular to the crankshaft indicate?

The difference in cylinder bore measurements taken parallel and perpendicular to the crankshaft indicates cylinder bore out-of-roundness. This condition occurs when the diameter of the cylinder bore is not consistent throughout its entire circumference.

When measurements are taken parallel to the crankshaft, you may find that the diameter differs from measurements taken perpendicular to it. If the bore is perfectly round, these two measurements should be nearly identical. However, significant discrepancies suggest that the bore has become out of round, which may lead to poor sealing of the piston rings and can cause engine performance issues such as loss of compression and increased oil consumption.

Cylinder bore taper, uniform wear, and valve clearance are associated with different aspects of engine wear and performance. Taper refers to a condition where the diameter changes along the length of the bore, uniform wear indicates evenly worn surfaces, and valve clearance relates to the gap between the engine valves and their seats, not the cylinder measurements. Therefore, the correct interpretation of measurement differences is directly tied to identifying out-of-roundness in the cylinder bore.